Method of coating a magnetostrictive matrix panel with a damping mass and resulting article



M r h 19. 1968 H J. H. VAN DEUTEKOM 3,

METHOD OF COATING A MAGNETOSTRICTIVE MATRIX PANEL WITH A DAMPING MASS AND RESULTING ARTICLE.

Filed July 6, 1964 S L w FIGJV v I -Hm Hm -----H INVENTOR. HUIBERT JACOBUS HENDRIK VAN DEUTEKOM United States Patent ()fiice 3,374,lli9 Patented Mar. 19, 1968 3,374,109 METHOD OF COATING A MAGNETOSTRICTIVE MATRIX PANEL WITH A DAMPING MASS AND REEaULTiNG ARTICLE Huibert .lacohus Hendrik van Deutekom, Emmasingel, Eindhoven, Netherlands, assignor to North American Philips Company, Inc., New York, N.Y., a corporation of Deiaware Filled July 6, 1964, Ser. No. 380,341 Claims priority, application Netherlands, July 12, 1963, 295,257 3 Claims. (Cl. 117-201) ABSTRACT OF THE DISCLOSURE The magnetostrictive vibrations in a magnetic core storage matrix panel are damped by coating matrix with a mixture of a high-molecular weight polyvinylbutyral resin and a plasticizer such as tricresolphosphate.

The invention relates to the production of a damped matrix by coating it with a damping mass suitable for damping mechanical vibrations at temperatures lying between about C. and about +80 C., which vibrations may occur, for example, in magnetic core storages as a result of the electric pulses applied to the storage.

A magnetic core storage usually comprises at least one matrix panels, each of which is formed by a number of toroidal cores arranged in rows and columns through which insulated electric conductors are threaded. A matrix panel may furthermore comprise so-called blocking wires and a read wire, which are treaded through the cores in a given, known pattern.

The cores are formed by rings usually consisting of an oxidic magnetic material having a substantially rectangular hysteresis loop.

When magnet cores are employed as storage elements, it is desirable that mechanical vibrations which may be performed by the cores under the action of the applied electric pulses owing to their magneto-strictive properties should be restricted as far as possible without adversely affecting the magnetic properties of the elements. The

magneto-strictive properties of the storage elements may result in that with certain patterns of information stored in the storage, the so-called worst pattern, reading may give erroneous informationv Besides, any motion performed by the cores with respect to the electric conductors under the action of vibrations from without may give rise to wear and breakage of the electric conductors.

The invention has for its object to produce matrix coated with a dampingmass which has a negligible influence on the electro magnetic properties of the cores, which clamps the magneto-strictive vibrations, which raises the resonance frequency of the matrix panel and the properties of which will not vary with time.

In accordance with the invention such a mass is obtained by making a mixture of a plasticizer and highmolecular polyvinylbutyral resin in a ratio by weight from 1:1 to 3:7 and a volatile, organic solvent in a quantity such that a workable mass is obtained.

Best results are obtained by using a polyvinylbutyral resin having a k-value of its intrinsic or own viscosity of at least 50.

A plasticizer providing by mixing with a polyvinylbutyral resin a damping mass of practical suitability must satisfy the following requirements:

(1) The softener must be miscible in adequate quantities with polyvinylbutyral resin and must remain miscible in such quantities in a wide temperature range.

(2) The vapour pressure of the softener must be low in the desired temperature range.

(3) In the desired temperature range the viscosity of the mixture of this softener with the polyvinylbutyral resin must be substantially constant.

( 4) The mixture must be self-extinguishing.

(5) The mixture must be removable for carrying out repairs.

(6) The mixture must be little aggressive or not at all.

It has been found that tricresylphosphate fulfils all these requirements in a particularly satisfying manner.

A mass according to the invention may be produced in the following manner.

100 gms. of tricresylphosphate is dissolved in 1000 mls. of ethanol; then 100 gms. of polyvinylbutyral resin is gradually added, whilst stirring, to the solution until the mixture is clear. A quantity of an organic colouring substance may be added to the mixture, in order to facilitate the application of the mass. Satisfactory results are obtained by using a polyvinylbutyral resin which has a k-value of its own viscosity of 50 to 55 (Fikentscher: Cellulose Chemie 13, pages 58 and if, 1932). This mass is preferably employed when the widest possible temperature range has to be covered, whilst very small cores are used. It may be used at temperatures lying between lO C. and +40 C. and for a short time up to C. At C. dripping effects do not yet occur. The mixture is self-quenching and does not maintain combustion even at very high temperatures. If the requirements are less severe or if cores of not too small dimensions are used, a smaller quantity of tricresylphosphate or of other plasticizer may suflice. In general, however, the quantity to be used will not be less than 30% of the total weight of the mixture of plasticizer and the polyvinyibutyral resin. Use is preferably made of a rapidly evaporating, nonaggressive or little aggressive solvent, for example methanol, ethanol and the like. The mass is applied to the matrix panel by casting, painting, dipping or the like. Then the solvent is evaporated for example by heating at about +70 C.

Other plasticizers which can be used include tricrelenylphosphate, cresyldiphenyl phosphate and tri-(2 ethyl henyl) phosphate.

The effect of the damping mass will be explained more fully with reference to the accompanying drawing and to measurements to be described hereinafter.

In the drawing FIG. 1 shows diagrammatically part of a matrix panel.

FIG. 2 shows an idealised hysteresis loop.

Referring to FIG. 1 reference numeral 19 designates the cores of oxidic ferromagnetic material X and Y designate the electric conductors used for recording: and reading the information. The arrows indicated near the conductors indicate for each conductor the direction in which the pulse has to be passed through the wire for writing information, Z is the blocking wire through which a pulse can be guided for reading in order not to loose information during reading and writing, so it is avoided that addi' tional information is written, when a plurality of matrix panels co-operate. S is the read wire. During reading pulses are introduced in said wire, from which pulses the information available in the matrix panel can be inferred. Owing to the manner of twisting of the wires disturbing pulses neutralise each other for the major part. With this manner of twisting the cores are divided into two groups of equal size, which supply pulses of opposite polarities, both when the magnetization in coreschanges over and when the magnetization varies under the action of pulses which are not sufiiciently great for producing the change-over of the magnetisation. When pulses are passed through the read wire S, the value of which suffers for changing over the magnetisation of the cores, a pattern of information is written in the matrix panel, which is known under the name of worst pattern. With such a pattern all cores inducing a positive pulse in the read wire at the changeover of the magnetisation are in a state of positive remanence and all cores inducing a negative pulse under the same conditions are in a state of negative remanence or conversely in accordance with the polarity of the pulses passed through the read wire, when this pattern is induced.

It is found that with such a pattern the neutralisation of disturbing pulses is at a maximum, whilst the residual signal due to the incomplete neutralisation is at the maximum.

With such a pattern the effect of a damping mass on the magneto strictive vibrations can be measured particularly satisfactorily from the disappearance of the vibration of the disturbing pulses on the read wire.

FIG. 2 shows the ideal hysteresis loop of a core associated with a given current strength Im corresponding to a field strength Hm. B+m is the maximum induction. B+r is the positive remanent induction. Br is the negative remanent and Bm' is the minimum induction. If the magnetic core is in the state of positive remanence 1 (B r), a pulse -Im corresponding to a field Hm will cause the path 172173 to be followed. When the field is removed, the magnetic core arrives in the state of negative remanence indicated as point 4 (E r). When a pulse +Im is passed through the conductors which corresponds to a field +Hm, the path 45186 is followed and after the removal of the field the core returns to the state of positive remanence. When a pulse /2Im is passed through one of the conductors of the core, corresponding to a field /2Hm: (for example in recording information in the matrix panel in a number of cores), for example the point M is reached. When the field /,:Hm is removed, the core arrives at the state of remanent induction 8, which is, however, lower than the initial remanent induction B+r. This process usually appears several times in a matrix panel. The permanent magnetic induction may then approach a limit value B rd. When a pulse -Im corresponding to a field Hm is passed through the conductors of the core, a flux variation occurs, which is proportional to the induction variation B -B+ Thus the read wire has produced across it a voltage pulse, the maximum value of which is indicated by rVl (read disturbed one). The usability of a damping mass has to fulfill the requirement that the maximum value of the voltage pulse across the read wires rVl, designated hereinafter by the rVl-signal, should not vary. A variation of the value of the signal would mean that the magnetic properties of the cores vary by the use of the damping mass.

In order to assess the favourable effect of the use of a damping mass prepared by the method according to the invention the following measurements were carried out:

(A) A matrix panel comprising 64x 64 toroidal cores 19 having an outer diameter of 1.27 mm. and an inner diameter of 0.76 mm. of oxidic, ferromagnettic material, the hysteresis loop approaches the rectangular shape, and provided with a wiring as shown in FIG. 1 was covered by a mass consisting of a mixture of equal parts by weight of tricresylphosphate and high-molecular polyvinylbutyral resin having a k-value of the natural viscosity between 50 and 55, as indicated above.

The resonance frequency of the matrix panel was prior to lacquering 44 c./ s.

After lacquering it was 59 c./s.

Two days after lacquering it was 72 c./s.

The resonance frequency was measured with the aid of a vibration table and .a stroboscope.

(B) Prior to and after the application of the damping mass to the matrix panel the so-called rVl signal was measured. The measurements were carried out at 0 C. Any influence of the damping mass on the magnetic properties of the cores is at this temperature greater than at room temperature at at a higher temperature. Im was at this temperature 596 ma.

It was found that the value of the rVl signal prior to and after the application of the damping mass and after ageing of the damping mass was substantially the same. It may be concluded therefrom that the influence of the damping mass on the magnetic properties of the cores is only very slight.

When silicon lacquers are used, said influence appeared to be so high, particularly after ageing-the rVl signal decreased by at least about 20%that this material is, in general, less suitable or not suitable at all.

(C) Prior to and after the application of the damping mass the residual signal due to the incomplete relative neutralisation of the disturbance pulses resulting from magnetostrictive vibrations of the cores was measured. It has been found in this respect that the noise of the read signal produced by pulses across the blocking wire has a magnetostrictive character. With a view to the magneticmechanical character of the vibration, it was found to be possible to damp mechanically these vibrations with the aid of the damping mass according to the invention. The measurements were carried out at C., since it has in general been found that the damping eifect of a damping mass decreases with an increasing temperature. The value of the pulse Im was, at +50 C. 470 ma. The measurements were carried out on a matrix panel of the kind described under A; it comprised a worst pattern of information. The read signal was measured whilst a sequence of identical pulses was passed through the blocking wire; each had a value of 259 ma. (amplitude of the amplitude of Im). The ratio between the voltage at the third vibration on the read wire due to the trailing edge of the pulse across the blocking wire was measured on a lacquered matrix panel and on a non-lacquered matrix panel. It was 1.5:13. The damping time, i.e. the time elapsing until the amplitude of the vibration is /s of the maximum amplitude, was 24 1.866. with a non-lacquered matrix panel and 3 ,usec. with a lacquered matrix panel. The frequency of the magnetostrictive vibrations was in both cases the same. Advantages of such a mass are furthermore, that it can be simply removed, for example by means of solvent, locally or wholly without damaging the matrix, for example for carrying out repairs and that it is self-extinguishing.

What is claimed is:

1. A method of producing a damped matrix by coating the matrix with a damping mass suitable for damping vibrations which may be produced in matrix panels, said damping mass comprising a mixture of a plasticizer and a high-molecular polyvinylbutyral resin in a ratio by weight of 1:1, to 3:7 and a volatile organic solvent in a quantity such that a workable mass is obtained.

2. A method as claimed in claim 1, characterized in the matrix is coated with a mixture of tricresolphosphate and polyvinylbutyral resin having a k value of its own viscosity of 50 to 55.

3. Damped matrix panels obtained by the method of claim 1.

References Cited UNITED STATES PATENTS 3,237,173 1/1962 Chamberlain et al. 340174 OTHER REFERENCES Polyisobutylen Guterbock Springer, Verlag/ Berlin 1959 (p. 178 relied on).

WILLIAM L. JARVIS, Primary Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,374,109 March 19, 1968 Huibert Jacobus Hendrik van Deutekom It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 2, line 71, "suffers" should read suffices Signed and sealed this 2nd day of December 1969.

(SEAL) Attest:

Edward M. Fletcher, Jr. E. JR.

' Commissioner of Patents Attesting Officer 

